The wait array used in synchronization primitives. More...

#include "sync0arr.h"
#include <sys/types.h>
#include <time.h>
#include "lock0lock.h"
#include "os0event.h"
#include "os0file.h"
#include "srv0srv.h"
#include "sync0arr_impl.h"
#include "sync0debug.h"
#include "sync0sync.h"

Macros
#define	sync_array_exit(a) mutex_exit(&(a)->mutex)

#define	sync_array_enter(a) mutex_enter(&(a)->mutex)

Functions
static bool	sync_array_detect_deadlock (sync_array_t arr, sync_cell_t cell, size_t depth)
	Detects a deadlock of one or more threads because of waits of semaphores. More...

static void	sync_array_validate (sync_array_t *arr)
	Validates the integrity of the wait array. More...

sync_cell_t *	sync_array_get_nth_cell (sync_array_t *arr, ulint n)
	Gets the nth cell in array. More...

static void	sync_array_free (sync_array_t *arr)
	Frees the resources in a wait array. More...

static os_event_t	sync_cell_get_event (sync_cell_t *cell)
	Returns the event that the thread owning the cell waits for. More...

sync_cell_t *	sync_array_reserve_cell (sync_array_t arr, void object, ulint type, ut::Location location)
	Reserves a wait array cell for waiting for an object. More...

void	sync_array_free_cell (sync_array_t arr, sync_cell_t &cell)
	Frees the cell. More...

void	sync_array_detect_deadlock ()

void	sync_array_wait_event (sync_array_t arr, sync_cell_t &cell)
	This function should be called when a thread starts to wait on a wait array cell. More...

template<typename Mutex >
static void	sync_array_mutex_print (FILE file, const Mutex mutex)
	Reports info about a mutex (seen locked a moment ago) into a file. More...

void	sync_array_cell_print (FILE file, const sync_cell_t cell)
	Reports info of a wait array cell into a file. More...

static sync_cell_t *	sync_array_find_thread (sync_array_t *arr, std::thread::id thread)
	Looks for a cell with the given thread id. More...

static bool	sync_array_deadlock_step (sync_array_t *arr, std::thread::id thread, size_t depth)
	Recursion step for deadlock detection. More...

template<typename Mutex >
static bool	sync_array_detect_mutex_deadlock (const Mutex mutex, sync_array_t arr, sync_cell_t *cell, size_t depth)
	A helper for sync_array_detect_deadlock() to handle the case when the cell contains a thread waiting for a mutex. More...

template<typename F >
bool	sync_array_detect_rwlock_deadlock (sync_cell_t cell, sync_array_t arr, const size_t depth, F &&conflicts)

static bool	sync_array_detect_deadlock_low (sync_array_t arr, sync_cell_t cell, size_t depth)

static bool	sync_arr_cell_can_wake_up (sync_cell_t *cell)
	Determines if we can wake up the thread waiting for a semaphore. More...

void	sync_array_object_signalled ()
	Increments the signalled count. More...

static void	sync_array_wake_threads_if_sema_free_low (sync_array_t *arr)
	If the wakeup algorithm does not work perfectly at semaphore releases, this function will do the waking (see the comment in mutex_exit). More...

void	sync_arr_wake_threads_if_sema_free (void)
	If the wakeup algorithm does not work perfectly at semaphore releases, this function will do the waking (see the comment in mutex_exit). More...

static bool	sync_array_print_long_waits_low (sync_array_t arr, std::thread::id waiter, const void *sema, bool noticed)
	Prints warnings of long semaphore waits to stderr. More...

bool	sync_array_print_long_waits (std::thread::id waiter, const void *sema)
	Prints warnings of long semaphore waits to stderr. More...

static void	sync_array_print_info_low (FILE file, sync_array_t arr)
	Prints info of the wait array. More...

static void	sync_array_print_info (FILE file, sync_array_t arr)
	Prints info of the wait array. More...

void	sync_array_init (ulint n_threads)
	Create the primary system wait array(s), they are protected by an OS mutex. More...

void	sync_array_close (void)
	Close sync array wait sub-system. More...

void	sync_array_print (FILE *file)
	Print info about the sync array(s). More...

Variables
ulong	srv_sync_array_size = 1
	User configured sync array size. More...

ulint	sync_array_size
	Locally stored copy of srv_sync_array_size. More...

sync_array_t **	sync_wait_array
	The global array of wait cells for implementation of the database's own mutexes and read-write locks. More...

static ulint	sg_count
	count of how many times an object has been signalled More...

Detailed Description

The wait array used in synchronization primitives.

Created 9/5/1995 Heikki Tuuri

Macro Definition Documentation

◆ sync_array_enter

#define sync_array_enter ( a ) mutex_enter(&(a)->mutex)

◆ sync_array_exit

#define sync_array_exit ( a ) mutex_exit(&(a)->mutex)

Function Documentation

◆ sync_arr_cell_can_wake_up()

static bool sync_arr_cell_can_wake_up ( sync_cell_t * cell )

static

Determines if we can wake up the thread waiting for a semaphore.

Parameters

cell	in: cell to search

◆ sync_arr_wake_threads_if_sema_free()

void sync_arr_wake_threads_if_sema_free ( void )

If the wakeup algorithm does not work perfectly at semaphore releases, this function will do the waking (see the comment in mutex_exit).

This function should be called about every 1 second in the server.

Note that there's a race condition between this thread and mutex_exit changing the lock_word and calling signal_object, so sometimes this finds threads to wake up even when nothing has gone wrong.

◆ sync_array_cell_print()

void sync_array_cell_print	(	FILE *	file,
		const sync_cell_t *	cell
	)

Reports info of a wait array cell into a file.

Parameters

[in]	file	File where to print.
[in]	cell	Sync array cell to report.

◆ sync_array_close()

void sync_array_close ( void )

Close sync array wait sub-system.

◆ sync_array_deadlock_step()

static bool sync_array_deadlock_step	(	sync_array_t *	arr,
		std::thread::id	thread,
		size_t	depth
	)

static

Recursion step for deadlock detection.

Parameters

[in]	arr	The wait array we limit our search for cycle to. The caller must own the arr->mutex.
[in]	thread	The thread which blocking other threads, which we want to find in the arr, to know if and why it's blocked, too
[in]	depth	The recursion depth

Returns: true iff deadlock detected (there might be false negatives)

◆ sync_array_detect_deadlock() [1/2]

void sync_array_detect_deadlock ( )

◆ sync_array_detect_deadlock() [2/2]

static bool sync_array_detect_deadlock	(	sync_array_t *	arr,
		sync_cell_t *	cell,
		size_t	depth
	)

static

Detects a deadlock of one or more threads because of waits of semaphores.

Reports a fatal error (and thus does not return) in case it finds one. The return value is only used in recursive calls (depth>0).

Parameters

[in]	arr	The wait array we limit our search for cycle to. The caller must own the arr->mutex.
[in]	cell	The cell to check
[in]	depth	The recursion depth

Returns: true iff deadlock detected (there might be false negatives)

◆ sync_array_detect_deadlock_low()

static bool sync_array_detect_deadlock_low	(	sync_array_t *	arr,
		sync_cell_t *	cell,
		size_t	depth
	)

static

◆ sync_array_detect_mutex_deadlock()

template<typename Mutex >

static bool sync_array_detect_mutex_deadlock	(	const Mutex *	mutex,
		sync_array_t *	arr,
		sync_cell_t *	cell,
		size_t	depth
	)

static

A helper for sync_array_detect_deadlock() to handle the case when the cell contains a thread waiting for a mutex.

Parameters

[in]	mutex	the mutex to check
[in]	arr	wait array; NOTE! the caller must own the mutex to array
[in]	cell	the cell which contains the mutex
[in]	depth	recursion depth

◆ sync_array_detect_rwlock_deadlock()

template<typename F >

bool sync_array_detect_rwlock_deadlock	(	sync_cell_t *	cell,
		sync_array_t *	arr,
		const size_t	depth,
		F &&	conflicts
	)

◆ sync_array_find_thread()

static sync_cell_t * sync_array_find_thread	(	sync_array_t *	arr,
		std::thread::id	thread
	)

static

Looks for a cell with the given thread id.

Returns: pointer to cell or NULL if not found

Parameters

arr	in: wait array
thread	in: thread id

◆ sync_array_free()

static void sync_array_free ( sync_array_t * arr )

static

Frees the resources in a wait array.

Parameters

arr	in, own: sync wait array

◆ sync_array_free_cell()

void sync_array_free_cell	(	sync_array_t *	arr,
		sync_cell_t *&	cell
	)

Frees the cell.

NOTE! sync_array_wait_event frees the cell automatically!

Parameters

arr	in: wait array
cell	in/out: the cell in the array

◆ sync_array_get_nth_cell()

sync_cell_t * sync_array_get_nth_cell	(	sync_array_t *	arr,
		ulint	n
	)

Gets the nth cell in array.

Parameters

[in]	arr	Sync array to get cell from.
[in]	n	Index of cell to retrieve.

Returns: cell

◆ sync_array_init()

void sync_array_init ( ulint n_threads )

Create the primary system wait array(s), they are protected by an OS mutex.

in: Number of slots to create

Parameters

n_threads in: Number of slots to create in all arrays

◆ sync_array_mutex_print()

template<typename Mutex >

static void sync_array_mutex_print	(	FILE *	file,
		const Mutex *	mutex
	)

static

Reports info about a mutex (seen locked a moment ago) into a file.

Parameters

[in]	file	File where to print.
[in]	mutex	The mutex to describe.

◆ sync_array_object_signalled()

void sync_array_object_signalled ( )

Increments the signalled count.

Note that one of the wait objects was signalled.

◆ sync_array_print()

void sync_array_print ( FILE * file )

Print info about the sync array(s).

Prints info of the wait array.

Parameters

file	in/out: Print to this stream

◆ sync_array_print_info()

static void sync_array_print_info	(	FILE *	file,
		sync_array_t *	arr
	)

static

Prints info of the wait array.

Parameters

file	in: file where to print
arr	in: wait array

◆ sync_array_print_info_low()

static void sync_array_print_info_low	(	FILE *	file,
		sync_array_t *	arr
	)

static

Prints info of the wait array.

Parameters

file	in: file where to print
arr	in: wait array

◆ sync_array_print_long_waits()

bool sync_array_print_long_waits	(	std::thread::id *	waiter,
		const void **	sema
	)

Prints warnings of long semaphore waits to stderr.

Returns: true if fatal semaphore wait threshold was exceeded

Parameters

waiter	out: longest waiting thread
sema	out: longest-waited-for semaphore

◆ sync_array_print_long_waits_low()

static bool sync_array_print_long_waits_low	(	sync_array_t *	arr,
		std::thread::id *	waiter,
		const void **	sema,
		bool *	noticed
	)

static

Prints warnings of long semaphore waits to stderr.

Returns: true if fatal semaphore wait threshold was exceeded

Parameters

arr	in: sync array instance
waiter	out: longest waiting thread
sema	out: longest-waited-for semaphore
noticed	out: true if long wait noticed

◆ sync_array_reserve_cell()

sync_cell_t * sync_array_reserve_cell	(	sync_array_t *	arr,
		void *	object,
		ulint	type,
		ut::Location	location
	)

Reserves a wait array cell for waiting for an object.

The event of the cell is reset to nonsignalled state.

Parameters

[in]	arr	wait array
[in]	object	pointer to the object to wait for
[in]	type	lock request type
[in]	location	location where requested

Returns: sync cell to wait on

◆ sync_array_validate()

static void sync_array_validate ( sync_array_t * arr )

static

Validates the integrity of the wait array.

Checks that the number of reserved cells equals the count variable.

Parameters

arr	in: sync wait array

◆ sync_array_wait_event()

void sync_array_wait_event	(	sync_array_t *	arr,
		sync_cell_t *&	cell
	)

This function should be called when a thread starts to wait on a wait array cell.

In the debug version this function checks if the wait for a semaphore will result in a deadlock, in which case prints info and asserts.

Parameters

arr	in: wait array
cell	in: index of the reserved cell

◆ sync_array_wake_threads_if_sema_free_low()

static void sync_array_wake_threads_if_sema_free_low ( sync_array_t * arr )

static

If the wakeup algorithm does not work perfectly at semaphore releases, this function will do the waking (see the comment in mutex_exit).

This function should be called about every 1 second in the server.

Note that there's a race condition between this thread and mutex_exit changing the lock_word and calling signal_object, so sometimes this finds threads to wake up even when nothing has gone wrong.

◆ sync_cell_get_event()

static os_event_t sync_cell_get_event ( sync_cell_t * cell )

static

Returns the event that the thread owning the cell waits for.

Parameters

cell	in: non-empty sync array cell

Variable Documentation

◆ sg_count

ulint sg_count

static

count of how many times an object has been signalled

◆ srv_sync_array_size

ulong srv_sync_array_size = 1

User configured sync array size.

◆ sync_array_size

ulint sync_array_size

Locally stored copy of srv_sync_array_size.

◆ sync_wait_array

sync_array_t** sync_wait_array

The global array of wait cells for implementation of the database's own mutexes and read-write locks.

Macros

Functions

Variables

Detailed Description

Macro Definition Documentation

◆ sync_array_enter

◆ sync_array_exit

Function Documentation

◆ sync_arr_cell_can_wake_up()

◆ sync_arr_wake_threads_if_sema_free()

◆ sync_array_cell_print()

◆ sync_array_close()

◆ sync_array_deadlock_step()

◆ sync_array_detect_deadlock() [1/2]

◆ sync_array_detect_deadlock() [2/2]

◆ sync_array_detect_deadlock_low()

◆ sync_array_detect_mutex_deadlock()

◆ sync_array_detect_rwlock_deadlock()

◆ sync_array_find_thread()

◆ sync_array_free()

◆ sync_array_free_cell()

◆ sync_array_get_nth_cell()

◆ sync_array_init()

◆ sync_array_mutex_print()

◆ sync_array_object_signalled()

◆ sync_array_print()

◆ sync_array_print_info()

◆ sync_array_print_info_low()

◆ sync_array_print_long_waits()

◆ sync_array_print_long_waits_low()

◆ sync_array_reserve_cell()

◆ sync_array_validate()

◆ sync_array_wait_event()

◆ sync_array_wake_threads_if_sema_free_low()

◆ sync_cell_get_event()

Variable Documentation

◆ sg_count

◆ srv_sync_array_size

◆ sync_array_size

◆ sync_wait_array